Plum

Redhumped Caterpillar

Scientific name: Schizura concinna

The redhumped
caterpillar is easily
recognized because of its striking appearance: the main body color is yellow
and is marked by longitudinal reddish and white stripes; the head is bright
red; and the fourth abdominal segment is red and enlarged. Redhumped
caterpillars pass the winter as full-grown larvae in cocoons on the ground. In
spring and early summer, moths lay egg masses on the undersides of leaves. Eggs hatch into larvae that begin feeding on leaves. There are at least three
generations each year in northern California.

Redhumped caterpillar can be a pest of plum orchards in the Central
Valley. Biological control and pruning is often sufficient to manage the pest;
use the monitoring guidelines below to determine need for treatment.

Biological Control
A number of
natural enemies attack redhumped caterpillars, frequently preventing them from
becoming destructive pests. Most common are two parasitic wasps: Hyposoter fugitivus, which forms a single pupal case that is white
with a black band around the middle, and a species of Apanteles, which forms a fluffy white mass of pupal cases.
Several general predators, including spiders,
lacewings, bigeyed bugs, and damsel bugs, occasionally feed
on caterpillar eggs and small larvae.

Cultural Control
On small
trees, cut out and destroy infested twigs.

Organically Acceptable Methods
Biological
and cultural control and Bacillus thuringiensis (Bt) sprays are
acceptable for use in an organically certified crop.

Monitoring and Treatment Decisions
Begin
looking for redhumped caterpillars in May, when eggs or larvae of the first
generation may be present. Check trees throughout the orchard, looking at the
undersides of leaves for egg masses or groups of small larvae. Skeletonized
leaves that turn brown may indicate the presence of redhumped caterpillars. If
you find larvae of the first generation, do not treat. Prune out and destroy
localized infestations. Monitor again in July for second-generation larvae and
for the presence of parasites before you make a treatment decision. Look for
parasite pupae among larval colonies. If 80% or more of the larval population
is parasitized, no treatment is needed. If parasitization is very low, prune
out and destroy infestations or treat infested trees. Infestations tend to be
very localized; so spot treatments usually suffice. Formulations of Bt are
effective against the larvae.

COMMENTS: Most effective on small caterpillars. Does not destroy natural enemies.

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For dilute applications, rate is per 100
gal water to be applied in 300–500 gal water/acre, according to label;
for concentrate applications, use 80–100 gal water/acre, or lower if the label allows.

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Restricted entry interval (R.E.I.) is the
number of hours (unless otherwise noted) from treatment until the treated
area can be safely entered without protective clothing. Preharvest interval
(P.H.I.) is the number of days from treatment to harvest. In some cases the
REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.

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Acceptable for use on organically grown produce.

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Not recommended or not on label.

1

Rotate chemicals with a different
mode-of-action Group number, and do not use products with the same
mode-of-action Group number more than twice per season to help prevent the
development of resistance. For example, the organophosphates have a Group
number of 1B; chemicals with a 1B Group number should be alternated with
chemicals that have a Group number other than 1B. Mode of action Group
numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at http://www.irac-online.org/.

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